The present invention relates to a method and an apparatus for observing or processing and analyzing substrates with an insulator formed thereon using a charged beam; and; more particularly, the invention relates to a method and an apparatus of the type described, which can prevent charged particles from accumulating in an insulator irradiated by the charged beam, as well as to detect secondary electrons generated from those substrates as secondary particles.
At present, a charged beam is used for observing or analyzing and processing minute areas on LSI circuits, masks, etc. However, the method and apparatus used heretofore for such objects have experienced a problem in that, when observing or analyzing and processing substrates with an insulator formed thereon using a charged beam, the charged particles of the irradiated charged beam are accumulated (charging up) on the surface of the object insulator, with a result that the charged beam is repulsed, causing the irradiation point of the charged beam to be shifted, thereby disabling the observation or analysis and processing of the substrate. On the other hand, there is a conventional method that uses an ion beam to achieve the above-described operations, as disclosed in the official gazette of Japanese Patent Laid-Open No. 61-248346. According to this method, an electron shower is irradiated in the ion beam irradiation area, thereby neutralizing electrons which may have accumulated on the surface of the object substrate. The surface of the substrate can thus be observed, analyzed, and processed using a scanning ion microscope image obtained by detecting secondary ions ejected from the substrate during ion beam irradiation.
Since the above conventional technique uses an electron shower, it is impossible to obtain images from secondary electrons detected as secondary particle images. Consequently, the surface of the object substrate can be observed only by images obtained from secondary ions detected as described above. Furthermore, this case also experiences a problem in that high contrast images cannot be obtained, since the amount of secondary ions is as low as a few percent of the primary ions. This is why the positioning accuracy during irradiation of the charged beam is lowered. On the other hand, the official gazettes of the Japanese Patent Laid-Open No. 1-119668, No. 57-170526, and No. 1-243449 have disclosed methods of preventing the above-mentioned problems. According to those methods, the insulator formed on the object substrate is transformed into a conductive material by exciting the electrons therein optically so as to prevent a charging-up from occurring in the insulator. And accordingly, this method makes it possible to obtain images with secondary electrons detected as images of secondary particles.
The official gazette of the Japanese Patent Laid-Open No. 1-119668 has also disclosed a method of irradiating the substrate with an ultraviolet beam having a difference of energy between the conductor bands of Si and SiO2 or a difference of energy between valence bands. According to this method, an energy must be injected in the interface between Si and SiO2 It is thus impossible to use a short wavelength light that cannot pass through SiO2. In addition, it is also difficult to apply the method to substrates, which tend to block the light applied to the interface due to having a light-proof film, such as a mask, etc., as well as substrates which are not made of a conductive material.
Another method of preventing the surface of a light-exposed substrate from charging-up is disclosed in the official gazette of Japanese Patent Laid-Open No. 57-170526. According to this method, an organic semiconductor provided with optical conductivity is used or a semiconductor provided with optical conductivity is coated on the object resist. This method also includes problems in that a coating process is needed, as well as the fact that the kinds of samples which are capable of use are limited; and so, the method cannot be used for masks, and the like.
The official gazette of Japanese Patent Laid-Open No. 1-243449 has disclosed another method of preventing such charging-up. According to this method, light for exciting the object insulator is applied obliquely, so charging-up is apt to occur at portions on the substrate which are not irradiated by the light due to the projections and depressions formed thereon. In addition, it is also difficult for this method to prevent charging-up at samples covered completely by an insulator and isolated mask patterns even when the electrons in the insulator are excited, since there is no concrete method for grounding the charged electrons.
Under such circumstances, it is an object of the present invention to provide a method and an apparatus with which it is possible to observe or analyze and process respective substrates with an insulator formed thereon accurately and easily by solving the above-described conventional problems.
What makes it difficult to observe images of secondary particles on a substrate with an insulator formed thereon is charged particles that are not grounded, but are accumulated (charging-up) in the insulator. And, those accumulated charged particles cause the irradiated charged beam to be repulsed.
This is why it is considered to be possible to prevent such the charging-up if the surface of the substrate is transformed into a conductive material and grounded. And, the present invention has achieved this object by irradiating a light having a wavelength for exciting the electrons in the insulator on the object substrate, thereby transforming the insulator into a conductive material due to the photoconductivity effect, and then grounding the charged particles from the grounded surface.
The present invention has also achieved the above objects by employing a method that uses a charged beam and includes the following steps. Concretely, the method includes a step of placing a sample covered at least partially by an insulator film on a sample stage provided in a sample chamber, a step of irradiating light, possibly as pulses on the surface of the sample while the sample is placed on the sample stage and the sample chamber is evacuated, a step for irradiating the charged beam on the surface of the sample, a step of irradiating a light like pulses in an area ranged from a charged beam irradiation portion to the surface of a member grounded in the sample chamber so as to excite the electrons in the material composing the insulator film, a step of detecting secondary particles generated from the surface of the sample irradiated by the charged beam, and a step of observing, processing, or analyzing the surface of the sample according to information provided by the secondary particles detected in the preceding step.
The present invention has also achieved the above objects by employing a method that uses a charged beam and includes the following steps. Concretely, the method includes a step of placing a sample covered at least partially by an insulator film on a sample stage provided in a sample chamber, a step of irradiating light, possibly as pulses on the surface of the sample while the sample is placed on the sample stage and the sample chamber is evacuated, a step for irradiating the charged beam on the surface of the sample, a step of irradiating a light like pulses in an area ranged from a charged beam irradiation portion to the surface of a member grounded in the sample chamber so as to excite the electrons in the material composing the insulator film, a step of detecting secondary particles generated from the surface of the sample irradiated by the charged beam, and a step of observing, processing, or analyzing the surface of the sample according to information provided by the secondary particles detected in the preceding step.
Furthermore, the present invention has also achieved the above objects with an apparatus that uses a charged beam and includes the following components. Concretely, the apparatus of the present invention comprises a charged beam source for emitting a charged beam, a focusing optical system for irradiating the charged beam on the sample by focusing a charged beam emitted from the charged beam source, a stage for holding the sample thereon, secondary particle detecting means for detecting secondary particles generated from the sample irradiated by the charged beam focused by the optical focusing means, and irradiating means for irradiating ultraviolet light, possibly as pulses, on the surface of the sample.
Furthermore, the present invention has achieved the above objects with an apparatus that uses a charged beam and includes the following components. Concretely, the apparatus of the present invention comprises a sample chamber provided with a sample stage on which a sample is placed, evacuating means for evacuating the sample chamber, a charged beam source for emitting a charged beam, a focusing optical system for focusing the charged beam emitted from the charged beam source, thereby irradiating a focused charged beam on the sample placed on the sample stage, secondary particle detecting means for detecting secondary particles generated from a sample irradiated by the charged beam focused by the optical focusing system, and ultraviolet light irradiating means for irradiating ultraviolet light, possibly as pulses, in an area ranged from a charged beam irradiation portion on the surface of the sample to the surface of a member grounded in the sample chamber.
According to the present invention, therefore, it is easy to observe, process, and analyze substrates with an insulator formed thereon. Especially, it is possible to detect and correct defects on phase shifting masks. Furthermore, even for substrates composed of only an insulator, it is possible to observe, process, and analyze those substrates if a grounded probe or conductor exists in the light irradiation area and is in contact with the substrate.